Hi @schwessinger! Thanks for your post and sorry for late reply!. Stencila Hub (which we are currently testing and should be able to make it widely available soon) will enable collaborating over the project (as in, the owner of the project will be able to give access to other users; the access can be at different levels - read/write etc).
When one of the users saves the changes they made, Stencila would create behind the scenes a commit (leveraging the powers of version control). Long story short, it will prevent overwriting changes but allow for saving what a user has edited.

Hello @schwessinger!. Our editor is based on Substance, a JavaScript library for web-based content editing, which has built-in support for real time collaboration like in Google docs. We have not yet enabled that but it’s something that we would like to make part of the Stencila Hub in addition to the access controls which @Aleksandra mentioned.